<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

    <!-- 准备好一个容器 -->
    <div id="test">
        <button id="btn_1">按钮1</button>
        <button id="btn_2">按钮2</button>
        <button onclick="test()">按钮3</button>
    </div>

    <script type="text/javascript">

        const btn1 = document.getElementById("btn_1");
        btn1.addEventListener('click', ()=>{
            alert("按钮1被点击了")
        });

        const btn2 = document.getElementById("btn_2");
        btn2.onclick = ()=>{
            alert("按钮2被点击了")
        }

        function test() {
            alert("按钮3被点击了")
        }
    </script>
</body>

</html>